Help on how to win more u

Hey guys I've lost my last 6 games and I really need help. All of these games Ive been forced adc and my support feeds or I get the lane I want and win lane but my whole team is feeding. I try to be nice and say things like, "we can still do this guys" or "good job you did really well there" but it really doesn't help and I don't know if I'm just picking the wrong type of game"draft pick" or me not warding or telling my teammates to do this or that. A rengar ults in 1v5 while I stand hopeless and he blames me for not going in when I'm a squishy kass. Can you guys give me some tips or just help on how to win more?